1. Field of the Invention
This invention relates to apparatus for controlling the withdrawal of pollutants from an industrial atmosphere and more particularly to an arrangement of pipes that extend downwardly from a pollution control hood to form a curtain for minimizing the volume of air drawn into the hood with the pollutants while permitting access to the area beneath the hood.
2. Description of the Prior Art
In a metallurgical process molten metal is transferred from a furnace through an inclined spout, an open trough, runner or the like into a transport vessel, such as a ladle or a hot metal car for movement of the molten metal to another furnace. In the past the outlet of the spout or the trough was open to the atmosphere so that the flow of the molten metal into the receiving vessel could be observed; however, current environmental regulations require that a pollution control hood be positioned over the trough and that the hood be equipped with fans for exhausting the gaseous and particulate pollutants emitted from the molten metal to prevent discharging the pollutants into the surrounding atmosphere. The hood cannot completely enclose the trough so as to prevent access to the trough. Consequently, the size of the motors, fans, air cleaners and the like installed in a pollution control hood is determined by the volume of air that must be withdrawn from above the trough to prevent the pollutants from entering the surrounding atmosphere.
One of the problems encountered in collecting gaseous and particulate pollutants by a pollution control hood is the capacity of the fans and the other air cleaning equipment to efficiently draw the pollutants out of the surrounding atmosphere. However, the capacity of the fans must be large if the space between the hood and the trough is open to the surrounding ambient air in order to create sufficient negative pressure to draw the pollutants into the hood. Thus, in order to reduce the capacity of the fans it is desirable to minimize as much as possible the volume of ambient air pulled into the hood by the negative pressure created by the fans and yet permit access to the trough.
U.S. Pat. Nos. 4,076,223; 4,094,496; and 4,097,029 disclose for steel converting apparatus an enclosure that surrounds a vessel for converting molten ferrous metal to steel. The enclosure cooperates with a smoke hood that is positioned in spaced relation above the opening into the vessel. A movable, rigidly constructed skirt is positioned in surrounding relation with the annular space between the bottom of the smoke hood and the top of the vessel. The skirt is a unitary structure composed of a plurality of tubes affixed in a side-by-side relation by intervening bar members and in an annular configuration. The skirt is vertically lifted by a hydraulic lift mechanism between a raised position to permit an indraft of air into the hood and a lowered position minimizing the flow of air into the hood. Consequently to permit access to the annular space above the vessel to observe the conversion operation in the vessel, the entire skirt must be lifted permitting pollutants to be discharged into the surrounding atmosphere.
U.S. Pat. No. 3,834,293 discloses equipment for conveying the products of combustion in a smelting furnace. A plurality of nozzles positioned around the periphery of the furnace are directed upwardly and compressed air is emitted from the nozzles to form a fluid wall or a screen to form an insulated chamber directed from the furnace to the pollution control hood. With this arrangement the combustion products are extracted from the surrounding atmosphere in a manner which permits the use of a hood of reduced size and power requirements.
An adjustable hood having a wide mouth for preventing excessive air infiltration into the furnace during a refining operation is disclosed in U.S. Pat. No. 3,205,810. An outer duct is adjustably positioned to vary the size of an annular passageway between the outlet of the furnace and the inlet to the exhaust hood. In this manner the volume of air flowing into the exhaust hood is controlled for the most economical operation of the fan associated with the hood.
U.S. Pat. No. 3,325,158 discloses a blast furnace stockline protective device that includes a plurality of arcuate plates that extend downwardly and around a bell-hopper. The plates are operable to protect the refractory lining of the blast furnace from the charge entering the furnace from the bell-hopper. The plates are individually suspended from the hopper and are easily replaced and are moved into and out of position relative to the refractory wall of the blast furnace.
There is need for pollution control apparatus operable to limit the volume of air drawn into a pollution control hood that extracts from an industrial atmosphere pollutants emitted during an industrial process, such as the pollutants emitted from molten metal when conveyed from the blast furnace or the like to a metal transporting vessel. While it has been suggested to minimize the flow of air into a pollution control hood so as to permit the use of pollution control equipment of reduced capacity, the prior art devices do not provide an enclosure that efficiently minimizes the inflow of surrounding air into the hood while permitting access to the space beneath the hood to observe the metallurgical process without discharging pollutants into the surrounding atmosphere.